Semiconductor devices, such as integrated circuitry (IC), are massively manufactured by fabricating hundreds or even thousands of identical circuitry on a single semiconductor wafer, and hundreds or thousands of such wafers daily using photolithography in combination with various other material additive and removal processes. After being fabricated, these semiconductor devices are subsequently electrically connected to external electrical testers through electrical contact devices, such as probe cards, so that they can be tested.
An electrical contact device, such as probe card, is an integral part of connecting device to connect IC devices on semiconductor wafer to external electrical components, such as a tester etc. One key component of the electrical contact device is the mechanical and electrical contact structure which makes the physical and electrical contact to the IC device on the semiconductor wafer. There are several standard contacts for the probe cards, including the epoxy ring contact, the blade contact, and the micro-spring contact. The epoxy ring contact and the blade contact are traditional contacting technologies, and the micro-spring contact is an emerging new technology which makes fine mechanical and electrical contacts using micro-electrical-mechanical-systems (MEMS) fabrication techniques, which are well known by those skilled in the art. While probe cards made from these standard contact technologies have adequately worked in the past, the trend in semiconductor IC testing is to use smaller and smaller electrical contacts to accommodate the greater number of circuitry on the semiconductor substrates. This poses difficulties for traditional epoxy ring contact and blade contact technologies, and also poses desires for improvement and new designs of the micro-spring contact technology.
An example type of fine pitch micro-spring contact is described in U.S. Pat. No. 5,613,861 to Smith et al. entitled “Photo lithographically Patterned Spring Contact”, which discloses a spring contact formed of a thin stressed metal stripe which is in part fixed to a substrate and electrically connected to a contact pad on the substrate. The free portion of the metal stripe not fixed to the substrate bends up and away from the substrate due to the intrinsic stress gradient inside the thin metal stripe. When the testing pad on a device is brought into pressing contact with the free portion of the metal stripe, the free portion deforms and provides compliant contact with the testing pad. The contact pad on the substrate is electrically connected to the testing pad on the device via the spring contact. A typical embodiment of the stress metal spring contact is schematically shown in FIG. 1a. The spring contact comprises an anchor portion 101 associated with an electrical contact or terminal 102 attached to a substrate or electrical component 103, and a free portion 104 with a spring tip 105. Another similar example is described in U.S. Pat. No. 7,126,220 to Lahiri et al. entitled “Miniaturized Contact Spring”, which also uses the stressed metal to form the core part of the spring contact, and discloses a method of increasing the yield strength and fatigue strength of miniaturized spring contacts by electroplating the spring contacts with high elastic modulus metal materials. Both disclosures are herein incorporated as references. This type of spring contacts may be used for fine pitch probe card applications. However, this type of spring contacts intrinsically suffers from some process deficiencies. First, the core part of this type of spring contacts is composited of a plurality of differently stressed films to have a stress gradient in the z-direction, yet to have overall neutral stress in plane. This brings the concern of stress control. Second, the released springs, prior to the electroplating, are fragile and easy to fracture during the following process. Third, the large tension force applied on the spring contacts during testing creates large stress on the spring bases anchored on the substrate, therefore causes tendency of de laminations and other failures, and raises concerns of reliability.
Another example type of fine pitch spring contacts by lithographical and MEMS fabrication techniques is U.S. Pat. No. 6,268,015 to G. Mathieu et al., U.S. Pat. No. 6,184,053 to B. Eldridge et al., and other patents issued to the same group, which discloses a method to form cantilever type discrete spring contacts by selectively removing and adding desired building blocks to form spring contacts. The spring contacts are fabricated individually or in a group and subsequently mounted on a functional substrate, such as semiconductor testing devices. FIG. 1b is a schematic cross-sectional view of such a cantilever type spring contact. The spring contact comprises of a tip 201 which is attached to a free standing element 202 which at one end is attached to a post 203, which is attached to an electrical contacting terminal 204, which is positioned on a functional substrate 205. Upon testing of an external device, the tip 201 is pressed on the testing pad on the external device, therefore the free standing portion 202 compliantly deforms. This invention avoids the use of highly stressed films. The problem of this type of spring contacts is that the spring contacts are too long. Shorter and smaller spring contacts are desirable for testing of new generations of IC devices. This type of spring contacts also raises concern of mechanical failure as the building blocks are only adhered together through adhesion.
In above two types of spring contacts, a spring contact has a tip at the end of the free standing portion, and an anchoring portion on the substrate at the other end of the spring contact. During operation of testing, the tip is pressed, and the spring is elastically deformed. The anchoring portion experiences high stress, therefore raises concern of the adhesion reliability of the anchoring portion. At semiconductor IC testing, a miniaturized spring contact, in its lifetime, is subjected to a large number, for example one million times, of contacting operations which subject the spring contact to various levels of stresses. A spring contact is required to withstand such stresses without failure.
Therefore, what is desired is a mechanism for maximizing spring contact reliability, especially the adhesion to the substrate, and maximizing the yield strength and fatigue strength of the miniaturized spring contact within the miniaturization requirement.
What is further desired is a method of easy manufacturing of such high performance array of spring contacts, without sacrificing any of the desired features.
The invention herein comprises several means to circumvent the problems associated with the above two types of spring contacts and provides solutions that allow easy manufacturing of spring contact arrays suitable for meeting the stringent requirements of wafer level IC testing. For example, it teaches a symmetric design of a spring contact with two anchoring portions to improve reliability performance; it also teaches a method of forming the spring contact using a continuous, zero-stress core member through the entire spring contact; besides these, the invention enables easy manufacturing of integrated fine pitch spring contact arrays, allows fabrication of spring contact arrays with extremely uniform spring height and other desired properties, as well as durability.